In semiconductor device processing, identification of defective devices is crucial. This is especially true directly before shipping devices to customers. Presently, most manufacturers mark defective devices which are already packaged by scribing, with a diamond tipped scribe, a symbol (such as an "X") on the packaging. Scribing is commonly practiced because this mark will not be removed by processing subsequent to the actual marking of the package. Examples of subsequent processing include a post packaging anneal which can be in excess of 300 C.; plating processing to plate the lead frames with a conductor (such as a metal); and package and lead frame clean up in acidic (pH around 1 to 3) and/or basic (pH around 11 to 14--probably closer to 12-13).
While the scribing of the plastic encapsulation to designate a bad device will survive these process steps, it is also very difficult to see. This is problematic because are large number of these packaged devices are processed simultaneously and it is difficult for an operator to readily sift through all of these devices are pull out all of the defective devices which are marked with the scribe d "X".
More specifically, all of these packaged devices are processed together because they are tied together by the metal structure which forms each device's lead frames (the metallic pins which extend from the packaged device). Hence, when a device is determined to be defective it is not immediately discarded because it would not be cost-effective to cut away the defective devices from the common metallic structure which forms the lead frames to each packaged device. lnstead, the defective devices are scribed so that after the packaged devices are separated from one another, a sorting process can be performed whereby the defective devices (indicated by the scribed mark) can be discarded. Due to the large number of packaged devices that must be sorted at any given time and the difficulty of discerning a scribed device from an unscribed device, this process is very time consuming, expensive and inefficient because several devices slip through this process and end up in the end users product.
Hence, there is a need for a method of marking these defective packaged devices which is readily discernable to a human eye or other detecting device.